388 THE OUTGO OF ENERGY 



about each root sever it from the spinal cord by 

 a cut on the proximal side of the thread. Stimu- 

 late each nerve with a very weak tetanizing cur- 

 rent. Note the different results obtained from 

 nerves arising at different levels of the cord. 

 Stimulation of the most anterior root causes 

 marked flexion of the limb ; stimulation of the 

 middle roots, extension and internal rotation ; 

 and of the most posterior, simple extension. 



In a frog whose nerves have not been cut 

 expose the spinal cord and stimulate it at differ- 

 ent levels in both directions along its length. 

 The various movements of the hind limbs are 

 localized at different levels of the cord. 



DISTRIBUTION OF SENSORY SPINAL NERVES 



Destroy the brain of a large frog with the 

 seeker. Expose the lower half of the spinal cord 

 by the method already described. On one side 

 cut the dorsal sensory root of the 8th spinal nerve 

 and on the other cut the sensory root of the 7th, 

 9th, and 10th. After the section of each root 

 test, the cutaneous sensibility of the limbs by 

 placing upon the skin small pieces of filter paper 

 (two mm. square) moistened, not dripping, with 

 0.2 per cent sulphuric acid. Make a map of the 

 anaesthetic areas in each leg, and note the lack 

 of correspondence. 



